1. Field of the Invention
This invention relates to a process for preparing 5-nitro-1,4,4a,9a-tetrahydroanthraquinone (hereinafter referred to simply as 5-nitrotetrahydroanthraquinone). 1-aminoanthraquinone which is important as a dye intermediate can be readily obtained by oxidizing 5-nitrotetrahydroanthraquinone to form 1-nitroanthraquinone and reducing the 1-nitroanthraquinone.
2. Description of the Prior Art
In the production of 1-aminoanthraquinone, it is the common practice to aminate anthraquinone-1-sulfonic acid which is obtained by sulfonation of anthraquinone. However, this amination process involves some environmental problems such as a bad working environment and a waste liquor treatment since mercury is essentially required as a catalyst for sulfonation.
Under these circumstances, there have been proposed many processes for the preparation of 1-aminoanthraquinone, including, for example, a process (West Germany, OLS 2162538) wherein 1-aminoanthraquinone is formed through 1-nitroanthraquinone obtained by nitration of anthraquinone with concentrated nitric acid, and a process (West Germany, OLS 2103360) wherein anthraquinone is nitrated with nitric acid in phosphoric acid to obtain 1-nitroanthraquinone, followed by reduction to yield 1-aminoanthraquinone. However, these processes are disadvantageous from an industrial point of view in that a large quantity of the waste acid must be treated in a suitable manner and that the processes involve formation of by-products such as dinitroanthraquinone, 2-nitroanthraquinone and the like, so that a purifying step or system which requires a great deal of labor and cost is essential for obtaining highly pure 1-aminoanthraquinone.
While, there have been proposed several other processes wherein 5-nitroanaphthoquinone is condensed with 1,3-butadiene to form 5-nitrotetrahydroanthraquinone, followed by oxidation to obtain 1-nitroanthraquinone. In this instance, according to N.N.Woroshtzov (Khim, Nauka i Prom., 5, 474-475 (1960), 5-nitronaphthoquinone is subjected to react with 1,3-butadiene in methanol to result 5-nitrotetrahydroanthraquinone, which is then isolated and oxidized by air in an alcoholic alkali solution to obtain 1-nitroanthraquinone. Further, the French Pat. No. 1,486,803 describes the production of 1-nitroanthraquinone by reacting 5-nitroanthraquinone with 1,3-butadiene in nitrobenzene and subjecting the resultant reaction solution to oxidation in the presence or absence of piperidine to obtain 1-nitroanthraquinone. 1-nitroanthraquinone obtained by these processes can be readily reduced into 1-aminoanthraquinone by an ordinary method.
In general, 1-aminoanthraquinone which is to be employed as an intermediate for dye is preferred to have a purity of greater than about 98 wt% and a 2-aminoanthraquinone content as low as 1 wt%. The above-mentioned prior processes have, respectively, the following problems for economically supplying 1-aminoanthraquinone with such high purity.
5-nitronaphthoquinone which is used as a starting material in these processes is generally prepared from 1,4-naphthoquinone by nitration. In the nitration, an isomer, 6-nitronaphthoquinone, is also secondarily produced, so that crude 5-nitronaphthoquinone obtained after the nitration generally contains 5 to 20 wt% of 6-nitroanaphthoquinone.
According to the supplemental test conducted by us, when 6-nitronaphthoquinone-containing 5-nitronaphthoquinone (hereinafter referred to simply as crude 5-nitronaphthoquinone) used as a starting material is subjected to condensation with 1,3-butadiene and to oxidation and reduction in accordance with the process of Woroshtzov using ethanol as a solvent, 6-nitronaphthoquinone is successively converted into 6-nitro-1,4,4a,9a-tetrahydroanthraquinone (hereinafter referred to as 6-nitrotetrahydroanthraquinone), 2-nitroanthraquinone, and 2-aminoanthraquinone, which contaminate corresponding 5-nitrotetrahydroanthraquinone, 1-nitroanthraquinoone, and 1-aminoanthraquinone, respectively, thus it being difficult to obtain highly pure 1-nitrotetrahydroanthraquinone, 1-nitroanthraquinone or 1-aminoanthraquinone. In order to obtain these compounds with high purity, it is undesirably necessitated to purify the starting material, the intermediate or the final product, in additional purifying steps.
In the process of the French Pat. No. 1,486,803, 5-nitrotetrahydroanthraquinone produced is directly subjected to oxidation, without isolation from reaction system, into 1-nitroanthraquinone. Accordingly, when crude 5-nitronaphthoquinone is used as a starting material, 6-nitroanaphthoquinone is converted into 2-nitronaphthoquinone through 6-nitrotetrahydroanthraquinone, thus contaminating 1-nitroanthraquinone and lowering the purity thereof. Further, it is difficult to obtain highly pure 1-aminoanthraquinone from the thus contaminated 1-nitroanthraquinone. This process also requires an additional step of purifying the starting material or the product so as to obtain highly pure 1-nitroanthraquinone or 1-aminoanthraquinone. In this connection, we have found as a result of an experiment that when crude 5-nitronaphthoquinone is condensed with 1,3-butadiene in nitrobenzene and the resulting product is separated or isolated from the reaction system by filtration, most of 6-nitrotetrahydroanthraquinone produced from 6-nitronaphthoquinone is removed in a state of being dissolved in the solvent, so that there can be obtained highly pure 5-nitrotetrahydroanthraquinone, from which 1-nitroanthraquinone or 1-aminoanthraquinone with high purity can be prepared. However, this process is also industrially disadvantageous in that the dissolution loss of 5-nitrotetrahydroanthraquinone in solvent is large, it's yield being considerably reduced.
In order to produce highly pure 1-aminoanthraquinone in an economical manner, it is desirable to prepare 1-aminoanthraquinone with high purity from crude 5-nitronaphthoquinone without purification of the starting material, an intermediate and an ultimate product. This is very hard to achieve by the above-mentioned prior processes.